U.S. patent number 4,535,731 [Application Number 06/491,705] was granted by the patent office on 1985-08-20 for device for automatically varying the timing of a camshaft.
This patent grant is currently assigned to Alfa Romeo Auto S.p.A.. Invention is credited to Ambrogio Banfi.
United States Patent |
4,535,731 |
Banfi |
August 20, 1985 |
Device for automatically varying the timing of a camshaft
Abstract
This invention relates to a device for automatically varying the
timing of a camshaft relative to the drive shaft of an internal
combustion engine, comprising an axially slidable splined sleeve
which connects the camshaft to its drive pulley, and is operated by
the engine lubricating oil in such a manner as to change the
angular position of said camshaft by way of valve means controlled
by an electromagnetic actuator as a function of at least one engine
parameter.
Inventors: |
Banfi; Ambrogio (Milan,
IT) |
Assignee: |
Alfa Romeo Auto S.p.A. (Naples,
IT)
|
Family
ID: |
11179948 |
Appl.
No.: |
06/491,705 |
Filed: |
May 5, 1983 |
Foreign Application Priority Data
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|
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May 17, 1982 [IT] |
|
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21313 A/82 |
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Current U.S.
Class: |
123/90.15;
123/90.17 |
Current CPC
Class: |
F01L
1/34406 (20130101); F02F 7/006 (20130101); F01L
2001/34433 (20130101) |
Current International
Class: |
F01L
1/344 (20060101); F02F 7/00 (20060101); F01L
001/34 () |
Field of
Search: |
;123/90.15,90.17,90.55 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Koczo; Michael
Assistant Examiner: Neils; Peggy A.
Attorney, Agent or Firm: Brown; Charles A. Brown; Charles
E.
Claims
I claim:
1. A device for automatically varying the timing of a camshaft
relative to the drive shaft of an internal combustion engine, the
camshaft being supported by bearings lubricated by pressurized oil
of the engine lubrication circuit, the camshaft being driven in
timed relation with the drive shaft by a toothed pulley rigidly
affixed with a tubular member, the device comprising a sleeve
movable axially within the tubular member in order to connect the
toothed pulley to the camshaft, the sleeve being constrained to the
tubular member by means of a straight toothed splined connection
and being constrained to the camshaft by means of a helical toothed
connection, an annular piston being rigidly affixed with the
sleeve, a circular plate being rigidly affixed with the camshaft,
the circular plate with the tubular member and the annular piston
forming a chamber, the chamber being integrally connected to the
engine lubrication circuit which feeds the pressurized oil to the
camshaft support bearings by passage means for permitting oil to
flow to the chamber, a presized orifice in said passage means for
controlling the rate of oil flow to said chamber, vent means
coupled to said passage means downstream of said presized orifice
for communicating the passage means to atmosphere, said vent means
including axially movable valve means for opening and closing said
vent means and thereby regulating the feed and discharge flow of
oil through the passage means, said vent means being normally open
to allow the discharge of oil from said chamber, the axially
movable valve means being operationally connected to an
electromagnetic linear actuator which receives a command in the
form of an electric signal from an electronic central unit in
response to signal received from prechosen engine parameter sensors
whereby the axially movable valve means moves to close the vent
means causing oil to flow to the chamber.
2. A device as claimed in claim 1, characterized in that the
electromagnetic actuator is provided with a mobile armature which
moves axially outwards when the electromagnetic actuator is
energized.
3. A device as claimed in claim 1 wherein the axially moveable
valve means is a slide valve element and includes elastic means for
retaining the slide valve element in said normally open position
whereby the vent means is vented to atmosphere and oil will be
discharged from the chamber.
4. A device as claimed in claim 1 wherein the axially movable valve
means is a slide valve element and the vent means forms an integral
part of the slide valve element.
Description
In internal combustion engines, the intake and exhaust valves are
known to open immediately before the commencement of the piston
intake or exhaust stroke, and close immediately after termination
of said intake and exhaust stroke. In this manner, the valves are
completely open at the beginning and end of the respective stroke,
to allow proper filling of the cylinders with fresh mixture, and
effective expulsion of the gaseous products of combustion.
Consequently, straddling the T.D.C. between the end of the exhaust
stroke and beginning of the intake stroke of any one piston there
occurs the so-called cross-over in which the exhaust valves and
intake valves are simultaneously open. Under these conditions,
backward flow of part of the exhaust gas from the explosion chamber
or from the exhaust duct into the intake duct can occur, either
because of the vacuum existing in said exhaust duct when the
throttle valve is rather closed, and/or because of the
back-pressure present in the exhaust duct. The consequence of this
backward flow is a lesser filling of the cylinders and thus a lower
engine efficiency.
However, under cross-over conditions there can also be a positive
pressure difference between the intake duct and exhaust duct, when
the throttle valve is very open, and because of the inertia of the
fluid column present in the intake duct and exhaust duct it can
happen that the air or the fresh mixture scavenges the explosion
chamber, so increasing cylinder filling and consequently improving
the engine efficiency.
Thus in order to optimise engine operation, it would be necessary
to provide modest cross-overs for small throttle valve openings,
and large cross-overs for large throttle valve openings, whereas in
the case of fixed timing of the intake and exhaust valves, the
efficiency can be optimised only for determined engine speeds.
However, the ideal method involving the continuous variation of the
valve timing with the different engine operating conditions is
rather complicated in practice, and those methods which allow
operation with certain prechosen timing values, each optimised for
a particular region of the range of operation of the engine, have
proved easier to effect and also somewhat advantageous.
There already exist devices of this type particularly suitable for
engines with overhead camshafts, which allow automatic variation of
camshaft timing relative to the drive shaft. Of the many types, one
which has proved particularly functional is a device formed by
disposing an axially mobile connection sleeve between the camshaft
drive pulley and the camshaft itself, and connecting said sleeve to
the one and the other by means of splined couplings comprising
straight teeth and helical teeth. An annular piston which can be
operated by the pressurised oil used for lubricating the engine is
rigid with the sleeve, so that different timings of the camshaft
relative to the drive shaft correspond with the different axial
positions assumed by said sleeve.
In these devices, the feed or discharge of the oil for operating
the annular piston is controlled by valves operated mechanically as
a function of a prechosen engine parameter, for example the engine
rotational speed as determined by a centrifugal sensor, or the
angular position of the feed throttle valve.
These known devices, in which the valves are operated mechanically,
allow only timing variation relationships which are fairly simple
and linear to be attained, and are therefore not very versatile. In
addition, they are not suitable for providing a wide range of
variation of the timing, both because of their bulk and, in
particular, because of the constraints imposed by the arrangement
of the parts.
The object of the present invention is an improvement in timing
variation devices of the described type, which obviates the
limitations of known devices.
According to the invention, the valve means which control the feed
and discharge of the oil for operating the annular piston are
operationally connected to an electromagnetic actuator, which
receives a command for closing said valve means in the form of an
electric signal emitted by a central electronic unit able to
process the signals fed by sensors of prechosen engine
parameters.
A device constructed in this manner is very precise and reliable
even though it is able to effect even complicated timing variation
relationships, as a function of one or more engine parameters, as
will be apparent by examining the accompanying FIGS. 1 and 2, which
show two preferred embodiments of the invention by way of
non-limiting example.
FIG. 1 is a view, partly in axial section, of one embodiment of the
device;
FIG. 2 is a view, partly in axial section, of a second embodiment
of the device.
In FIG. 1, the reference numeral 10 indicates the partly shown
cylinder head of an internal combustion engine, and 11 indicates
the cylinder head cover. The cylinder head comprises the half
bearing 12 which supports the journal 13 of the camshaft 14, which
is also shown partly. The other half bearing 15 supporting the
journal 13 is formed in the cap 16.
A hollow pin, indicated by 20, is made rigid with the shaft 14 by
means of the screwed connection 19, and is provided at one end with
the flange 21 on which the tubular member 22 is mounted. The
toothed pulley 23 is made rigid with the tubular member 22 in known
manner, and is rotated by the drive shaft by means of a chain, not
shown.
The tubular member 22 is provided with a clutch 24 with internal
toothing of the straight toothed type, with which there engages
corresponding toothing 25 of a sleeve 26 rigid with an annular
piston 27, and also carrying toothing of the helical toothed type
indicated by 28, which engages with a corresponding clutch 29 with
external toothing, provided on the hollow pin 20.
The reference numeral 30 indicates a circular plate fitted with a
notched ring 31 for gripping purposes, and provided with a pin 32
which is made rigid with the hollow pin 20 by means of the screwed
connection 33.
The reference numeral 34 indicates a preloaded spring disposed
between the flange 21 and the ring 18 inside the sleeve 26.
The cylinder head 10 is provided with the duct 35 for feeding
lubricating oil to the half bearings 12 and 15 by way of the
annular cavity 36. The cap 16 comprises a threaded bore 37 into
which is screwed the stud 38, provided with a through bore 39 for
conveying the oil to discharge. The presized orifice 40 provided
for maintaining the lubricating oil to the half bearings 12 and 15
under pressure, is inserted into the bore 39.
The cap 16 is also provided with the bores 41 and 42, which connect
the bore 39 to a semi-annular cavity 43 provided in the pin 13. The
cavity 43 communicates by way of the radial bore 44 with the
longitudinal bore 45 provided in the shaft 14. The oil present in
the bore 39 can thus pass into the cavity 46, into the bores 47 and
48, and through the spaces between the teeth of the clutches 28 and
29, to reach the annular chamber 17 and the face of the annular
piston 27.
The figure shows the channel 49 which distributes the pressurised
oil in the left hand region of the half bearings, where the
pressure would be lacking due to the presence of the semi-annular
cavity 43, which being connected to the discharge bore 39 contains
oil at atmospheric pressure, except when the discharge is shut
off.
The connector 50, which is supported in the cylinder head cover 11,
is screwed onto the stud 38. The connector 50 is provided with oil
bleed bores 51 and 52 which communicate with the outside through
the bores 53 and 54 provided in the plate 55, and through the bore
56 provided in the cover 11.
The slide valve element 57, for shutting-off the bleed bore 54, is
mounted slidably in the bore 53. The valve element 57 leaves the
bleed bore 54 open when held back by the spring 58.
It should be noted that the bore 41 for the entry of oil to the
feed circuit for the chamber 17 and annular piston 27 branches from
the downstream side of the presized orifice 40, so that in said
circuit the pressure is atmospheric while the bleed bore 54 is
open, and increases to assume the value in the duct 35 only when
said bore 54 is closed.
The valve element 57 can be engaged by the mobile armature 59 of an
electomagnetic actuator 60, which is supported by the bracket 61
rigid with the plate 55 by way of the rubber ring 62, bolts 63 and
the cylindrical casing 64.
The coil of the electromagnet 60 is connected by the conductor 65
to a central electronic unit represented by the block 66 and
constituted for example by a unit comprising comparators able to
process the signals fed by sensors of prechosen engine parameters,
such as the angular position of the feed throttle valve, the vacuum
at the engine intake, the engine rotational speed, and the intake
air throughput.
In this particular case, the engine parameter used by the central
unit 66 to form the electromagnet control signal is the angular
position of the throttle valve, represented by the arrow 67.
The central unit 66 feeds no control signal to the electromagnet 60
while the indication of the angular position of the throttle valve,
represented by the arrow 67, is less than a predetermined threshold
value. In this case, the electromagnet is unenergised, and the
armature 59 remains in its withdrawn position as shown in FIG. 1,
the valve element 57 is held back by the spring 58, and the bore 54
remains open to connect to atmosphere the circuit (41, 42, 43, 44,
45, 46, 47, 48) for feeding oil to the chamber 17 and to the
annular piston 27.
Under these conditions, the sleeve 26 is urged by the spring 34
into its end position shown in FIG. 1, and is rotated by the
toothed pulley 23 by way of the coupling formed by the straight
teeth 24 and 25, to in its turn rotate the camshaft 14 by way of
the coupling formed by the helical teeth 28 and 29, to provide a
determined initial timing between the camshaft and toothed pulley
23.
The central unit 66 feeds a signal for causing the energising of
the electromagnet 60 when the indication of the angular position of
the throttle valve (arrow 67) exceeds a predetermined threshold
value. As a result of the energising of the electromagnet, the
armature 59 is thrust outwards and acts on the actuator 57 in the
sense of closing the bleed bore 54.
In the oil feed circuit (41-48) to the annular piston 27, the
pressure increases and assumes the value existing in the duct 35,
when the bleed bore 54 is completely closed. The pressurized oil
then acts on the annular piston 27 with a force which succeeds in
overcoming the preloading of the spring 34, and urges the sleeve 26
towards the right (in FIG. 1).
The axial movement of the sleeve 26, allowed by the coupling
provided by the straight teeth 24 and 25, leads to a corresponding
rotation of the hollow pin 20 by virtue of the presence of the
coupling formed by the helical teeth 28 and 29. Consequently, the
angular position of the camshaft 14 varies relative to the toothed
pulley 23, and thus the timing of the camshaft is changed relative
to the drive shaft. If the camshaft 14 is for example that which
controls the exhaust valves of an engine with overhead camshafts, a
variation is attained in the cross-over, for example an increase,
between the intake valves and exhaust valves, when the opening of
the throttle valve exceeds a predetermined value.
The control signal for the electromagnet 60 can also be provided by
the central unit 66 as a function of the combination of several
suitably chosen engine parameters.
In addition, if necessary, the electromagnet armature 59 and the
valve element 57 can be connected together by way of a linkage, for
example a rocker arm, in order to obtain force amplification.
FIG. 2 shows a modification of the device illustrated in FIG. 1,
the common elements being indicated by the same numerals.
In this case, the stud 38 is solid, and the connector 50 is without
bleed bores, while the plate 30 is in the form of a disc and the
pin 32 rigid therewith is hollow. In its internal bore 68 there is
disposed a slide valve element indicated by 69, provided with a
longitudinal dead bore 70 and radial bleed bores 71 and 72. On the
slide valve element 69 there acts a preloaded spring indicated by
73, which rests against a plug 77 and urges the valve element
against the disc 74, which is rigid with a rod 75 slidable in a
sealed manner in the wall of the cover 11.
The rod 75 can be engaged by the armature 59 of the electromagnetic
actuator 60, which is also supported by the cover 11 by means of
the bracket 76.
The device shown in FIG. 2 operates as that shown in FIG. 1. While
the slide valve element 69 is in a position pushed out of the bore
68 by the spring 73, the oil fed by the duct 35 is discharged to
the outside through the bores 70 and 72. Under these conditions,
the camshaft assumes a determined initial timing relative to the
toothed pulley 23.
When the armature 59 of the electromagnet 60 is urged outwards, the
slide valve element 69 is pushed into the bore 68, so shutting-off
the bleed bore 72. The pressurised oil then acts on the annular
piston 27 in order to vary the timing of the camshaft 14 relative
to the toothed pulley 23.
* * * * *